Help me troubleshoot my SBR! (PICS ADDED)

[1911-A1]

I took the 7.5" SBR to the range today. I was shooting 55gr American Eagle XM193BL The "AR 556 Tactical" black 100rd bulk box) and PMC 55gr brass cased ammo. The upper is from M&A parts (from years back, before I knew about no-name components, unfortunately) It's actually been very reliable and accurate, but it's not something I'd use for HD or take to a class.

The XM193 had multiple FTE problems which also caused doublefeeds, effectively turning my gun into a single-shot. The rounds felt underpowered as well, and failed to lock the bolt to the rear.

The PMC fed and fired fine, though. It was much softer shooting than the 193 and had no issues.

The question I have is: How are the reports about the A5 kit with 7.5" guns? I've shot tons of steel cased ammo through the upper with just a carbine and later an H2 buffer, all with no issues. This is the first time I've tried the 7.5" with the A5. My BCM 11.5" upper works great with it, though.

I am leaning toward this being ammo-related, since we had two different brands that performed differently in the same gun. I might contact Federal and see about getting the ammo replaced.

[Underwhere]

In my experience XM193 runs pretty hot.

Sorry no comments on how to fix this. I've never dealt with SBR's.

[Boss Hogg]

I would try a different bolt carrier first- or just go back to a regular receiver extension. Does the gas block have a good seal? Any rearward streaking on the barrel?

SBRs can be incredibly finicky and extraordinarily frustrating, mainly due to gas issues.

[Nefarious79]

Did you detail strip/clean your bolt?
Do you have an extractor booster/Oring installed?

[Tweak]

This is a new problem?

Most likely the 193 is hotter and causing the bolt to open too early while chamber pressure is holding the case walls to the chamber. You should clean the chamber and check the headspace just to be sure. Short stroke test it too.

A beefed up extractor and increasing the mass of the recoiling parts will help.

[SHULTZ]

Due to you saying that the rounds felt "softer", and that this problem just recently arose(?), I would take a close look at the gas system.

If there are no apparent gas issues, i would try a new BCG, specifically Daniel Defense.

Thats all I got for ya. Good luck.

[Iraqgunz]

just curious. Why would you recommend a new BCG? He could simply replace the bolt. In addition we haven't even determined what is actually wrong.

Due to you saying that the rounds felt "softer", and that this problem just recently arose(?), I would take a close look at the gas system.

If there are no apparent gas issues, i would try a new BCG, specifically Daniel Defense.

Thats all I got for ya. Good luck.

[Iraqgunz]

Am I to understand that this was working and then you dropped it onto a lower with an A5 set up?

I would do the following;

1. Check the bolt carrier key- looseness and anything inside it.

2. Check your extractor and ejector. The extractor should be stuff, but not overly so. The same with the ejector.

3. Possibly look at replacing the gas tube.

How many rounds does the upper have through it?

When did it very function correctly and what configuration was it in?

What mods have you done to it?

I took the 7.5" SBR to the range today. I was shooting 55gr American Eagle XM193BL The "AR 556 Tactical" black 100rd bulk box) and PMC 55gr brass cased ammo. The upper is from M&A parts (from years back, before I knew about no-name components, unfortunately) It's actually been very reliable and accurate, but it's not something I'd use for HD or take to a class.

The XM193 had multiple FTE problems which also caused doublefeeds, effectively turning my gun into a single-shot. The rounds felt underpowered as well, and failed to lock the bolt to the rear.

The PMC fed and fired fine, though. It was much softer shooting than the 193 and had no issues.

The question I have is: How are the reports about the A5 kit with 7.5" guns? I've shot tons of steel cased ammo through the upper with just a carbine and later an H2 buffer, all with no issues. This is the first time I've tried the 7.5" with the A5. My BCM 11.5" upper works great with it, though.

I am leaning toward this being ammo-related, since we had two different brands that performed differently in the same gun. I might contact Federal and see about getting the ammo replaced.

[1911-A1]

Am I to understand that this was working and then you dropped it onto a lower with an A5 set up?


Yes, it had a carbine and later an H2 buffer in a MilSpec RE before this.

I would do the following;

1. Check the bolt carrier key- looseness and anything inside it.

seems solid, staked properly.

2. Check your extractor and ejector. The extractor should be stuff, but not overly so. The same with the ejector.

Both seem fine. Comparable to my BCM bolt.

3. Possibly look at replacing the gas tube.

How many rounds does the upper have through it?

I'd guess around 1k. It's just a plinker. I've had it since 2006.

When did it very function correctly and what configuration was it in?

It ran fine with the carbine and H2 buffers and all types of ammo (steel cased, .223, M193, M855) before I installed the A5 kit. However, PMC runs fine with the A5, the problem seems to be with the AE XM193BL 5.56mm ammo.

What mods have you done to it?


Lately? Nothing.
It's a home build gun with a no-name bolt/carrier/barrel, so I added the low-pro gasblock years ago which has always run fine. The only thing I've changed lately is the A5 kit and the different ammo.

Has anyone tried an A5 on a 7.5" gun? There always seemed to be plenty of gas to run it with the other buffers/springs.

[Iraqgunz]

I would be inclined to believe that the ammo could be the issue.